1. Field of the Invention
The present invention relates to a manufacturing method of a wiring substrate, and particularly relates to a manufacturing method of forming a wiring structure on a supporting base and using the wiring structure as a wiring substrate. The present invention is suitable for application to manufacturing of a wiring substrate for an interposer used when a semiconductor element is mounted.
2. Description of the Related Art
In recent years, as means for realizing a function equal to that of a so-called SoC (System-on-Chip) equipped with an advanced system function on one semiconductor chip (element), a format called a so-called SiP (System-in-Package) attracts attention. This SiP realizes systematization by enclosing plural LSI chips in a single package and aims at finally realizing the function equal to that of the SoC at low cost.
The aforementioned SiP requires a wiring substrate containing high-density wirings in order to electrically connect plural LSI chips to each other and form a more downsized system. Generally, as this substrate, a ceramic wiring substrate, a printed substrate, a flexible substrate, a silicon substrate, or the like is used.
Out of the aforementioned wiring substrates, the flexible substrate is formed by forming a metal wiring layer on the surface of a resin film made of an organic insulator material and stacking these layers. This kind of substrate has excellent manufacturing performance in that it has flexibility. The silicon substrate needs to have through-holes to electrically connect its front and back surfaces although the finest wirings can be formed.
In the SiP which is used for portable equipment, such a wiring substrate is used a lot because of a demand for downsizing, weight reduction, and low cost. “ALIVH” (product name) manufactured by Matsushita Electric Industrial Co., Ltd. is an example of conventional wiring substrates. This “ALIVH” is realized by stacking plural substrates in each of which wirings and via holes filled with conductive paste are formed in an insulating resin.
This “ALIVH” has a problem that scaling down is difficult although low-cost manufacturing is possible, and moreover design flexibility is limited. To solve this problem and realize scaling down, low cost, and design flexibility at the same time, for example, it is effective to form a wiring structure on a supporting base made of silicon, separate the formed wiring structure, and use it as a wiring substrate.
(Patent Document 1)
Japanese Patent Application Laid-open No. 2001-9202
(Patent Document 2)
Japanese Patent Application Laid-open No. 2003-309215
In the aforementioned Patent Document 1 and Patent Document 2, methods of separating a wiring structure formed on a supporting base from the supporting base are disclosed, respectively.
In a technique disclosed in Patent Document 1, an adhesive layer having an opening which is a portion intended for formation of the wiring structure (a resin thin film multilayer circuit film) on the supporting base (a supporting substrate 11 in FIG. 4), and the wiring substrate is formed thereon. After an outer peripheral portion of the adhesive layer of the wiring structure is separated from an inner portion thereof on the supporting base, the wiring structure is stripped from the supporting base to form a wiring substrate (a flexible thin film multilayer circuit 21).
In the aforementioned method, however, in a final step, it is necessary to strip the wiring structure from the supporting base by applying ultrasonic waves or sticking an adhesive tape to the surface of the wiring structure, which may damage the wiring structure.
A technique disclosed in Patent Document 2 is a method of providing an etch-back layer (an etch-back layer 2) which has Cu as its main component and can be removed by etching between the supporting base (a base substrate 1 in FIG. 3) and the wiring structure (a multilayer wiring substrate 44) and separating the wiring structure from the supporting base by dissolving the etch-back layer by etching. In the aforementioned method, however, a long time is required until the etch-back layer 2 is completely etched to its inner portion, so that the possibility of causing a problem that a material composing the wiring structure is damaged or degenerated by an etching solution during etching or the like is high. Moreover, even if degeneration can be avoided, a problem that mass productivity in manufacturing is low still remains.
Incidentally, in addition to the aforementioned methods, among methods of separating the wiring structure from the supporting base is a method of using a silicon wafer as the supporting base and removing the silicon wafer itself by grinding and etching. Alternatively, it is also possible to use a metal plate made of aluminum or copper as the supporting base and remove aluminum or copper by etching.
In either of these methods, there is a disadvantage that the cost of the supporting base is reflected in manufacturing cost, in addition, an enormous amount of unnecessary dust is generated in a manufacturing process including a case where a residue left after the silicon wafer is ground becomes dust just as it is, so that an influence on the environment cannot be ignored.
Further, a method of forming the wiring structure, then thinning the supporting base by grinding it by a grinder or the like, and dissolving a thin film of the remaining supporting base by an acid or the like is also thought, but also in this method, a large amount of unnecessary dust is generated in the manufacturing process, and hence the aforementioned problem remains unsolved.